1. Field of the Invention
The present invention relates to the field of mineral breakers and, more particularly, to the replaceable tip holders for rotors in centrifugal mineral breakers.
2. Description of the Prior Art
Centrifugal mineral breakers, such as that described in U.S. Letters Pat. No. 3,970,257, have provided the rock crushing industry with an efficient and remarkably effective alternative to the large and capital-intensive rock crushing apparatus previously used. The principle of such vertical shaft impacters is that mineral material fed axially into a rotor is flung outwardly at high speed into a housing surrounding the rotor. Due to the particular configuration of nonradial blades of the rotor housing, the material first ejected is retained and used as a rock lining to protect the walls and other parts of the rotor. Thus the breakdown of the rock is caused in great part by the forces of the rock impacting other rock rather than the parts of the machine.
Most of the parts in such a rotary mineral breaker are adequately protected from wear by the rock lining, except the surfaces located near the discharge ports, which face erosion from the passage of the mineral material on its discharge route from the rotor. Replaceable tip plates with inserts of wear-resistant material, such as tungsten carbide, in the tips have been used near these ports to address this problem. Backup plates with tungsten tips have also been used to protect the rotor in the event that the outer tip plates start to fail and the damage goes unnoticed or uncorrected until the tip plate has completely deterioriated. The tip plates have been found to frequently wear more extensively in the center section, which resulted in discarding the unused portions of the tungsten carbide located at the outer edges. Since tungsten carbide inserts are relatively expensive, the practice of splitting the outer tip plates into two "split tips", which could be interchanged rather than replaced, was developed and is described in U.S. Letters Pat. No. 4,586,663.
However, even these advances in the prior art do not solve all the problems of tip wear, since the stresses and deteriorating forces on these tips during operation of a vertical shaft impacter are extreme. First of all, the tip and tip plate must withstand constant abrasion of the rocks passing over the tip, and although the abrasion-resistant insert material can resist this erosion, over time the surrounding metal holder which supports the tungsten carbide in place cannot.
There is also a problem with slip streaming, which occurs when fine material, such as sand, begins to pass through joints or cracks in the tip plate and wears away the surrounding material. Since the conventional tip plate has a rectangular groove which holds a series of rectangular tungsten inserts, rather than one piece, there are numerous joints where slip streaming can occur, such as between the tungsten and the metal, between the tungsten inserts themselves, and between the split tip plates. Applicants are aware of one person's attempt to strengthen the resistance of the tip holder and increase its life by affixing numerous, relatively large cylindrical tungsten carbide inserts together in the abrasion-receiving end of the tip holder with an adhesive matrix, the tungsten inserts being disposed so that the cylindrical ends faced the rock flow and the wear. Despite the costliness of a tip holder with such a large quantity of tungsten, the tip did not wear well and failed because of slip streaming. Thus, the increased use of tungsten in the tip holder, by itself, has not solved the problems of tip wear.
Although the tungsten carbide inserts in the tips resist abrasion, they are vulnerable to impact and they may crack or chip when struck by tramp metal or other non-crushable material found in most mineral feeds. When tungsten carbide is struck by such tramp material, the crack can extend through its entire depth in the holder. Once there is a crack, the integrity of the tungsten is compromised and it is not as resistant to abrasion and slip streaming and ultimately, the tungsten pieces can even fall out of the holder.
Obviously, it is desirable to replace a damaged tip plate as soon after such a failure as possible, so that the backup tip and the parts of the rotor are not damaged as well. Moreover, when one tip is damaged by a component of the mineral feed, the others will frequently fail shortly thereafter from the same cause. Although the tip holder is replaceable, it is usually an effort to do so, since the bolt anchoring the tip holder to the backup plate of the rotor frequently becomes stripped and the rock bank must be chipped away to allow the necessary tools to be inserted to hold the bolt head. It can be appreciated that since replacing tips results in an interruption of the work cycle and may involve substantial down time, the procedure is desirably delayed until the end of a shift. But if such maintenance is deferred too long, the entire tip will be deteriorated and the rock flow will begin to wear away the backup tip, thereby increasing the expense of replacement and the risk of damage to the rotor as well. Thus, there is a need in the prior art for a tip holder which will provide wear and impact resistance at the point where protection is needed the most and one which will provide for controlled deterioration once damage has occurred. There is also a need to reduce the down time required for changing the tips and to reduce the weight of the part without decreasing its strength.
In rotary mineral breakers of this type it is necessary to adjust the configuration of the bank of rock material lining the interior wall, called the rock wave, to ensure that the parts of the rotor, including the tip holder, are adequately protected. Since the build up of the material and the wear pattern on the tip differ for different kinds of feeds and varying conditions of the rotor, regular rotor tune-up is required, and generally, the trail plates, which are vertical nonradial plates in the rotor, have to be adjusted to accommodate changes in the feed. A frequent problem resulting from an incorrect rock wave pattern is the deterioration of the uncovered portion of the tip holder contacted by the rock before it passes over the tungsten carbide. There is thus a need for a tip holder which can be designed to respond to different mineral types and sizes.
In addition, prior art tip holders limit the size and tonnage of minerals which can be processed in rotary mineral breakers of this type. Coarser materials have typically caused premature failure of the standard tip plate because of the tip holder's inability to resist wear and impact and to retain larger size rocks in the rock lining of the rotor. Thus, there is a need for a tip holder having long life which can be used successfully with coarser materials, as with well as smaller, finer ones and one which can withstand the bending forces of a high tonnage operation.
Accordingly, there is a need for a tip holder which can withstand centrifugal and bending forces and remain in a secured position, yet be easily removable when necessary. There is a need for a tip holder which can resist wear and in which any damage caused by impact forces can be controlled to prevent total part failure. Most importantly, there is a need in the state of the art for a tip holder which can be used effectively for an extended time without requiring replacement and the resulting down time. There is also a need for a tip holder which can be designed to meet the requirements of different mineral feeds without the need for critical adjustments of the other parts of the rotor and one which will allow larger, coarser minerals to be processed by the rotor.
The present invention provides a tip holder which meets these needs and is a solution to these problems of the prior art. The present invention provides a part which has quadrupled the life of a conventional part and one in which deterioration of the part is controlled and the part retains structural integrity, even if normal consumption occurs. The tip holder of this invention fully utilizes the costly tungsten tips in the part before failure; it is also lighter weight and easier to replace. In addition, the tip holder of the present invention can be adapted for use with a wide variety of mineral feeds and can be used with larger, coarser minerals and with higher tonnage throughputs than rotary mineral breakers of this type customarily process.